Piezo-electric acoustic device



Aug. 23, 1932. A. MEISISNE'R 1,373,715

PIEZO ELEdTRIc ACOUSTIC DEVICE Filed July 26, 1928 INVEN TOR ORNEY Patented Aug. 23, 1932 V UNITED STATES PATENT oFFIcE ALEXANDER MEISSNER, OF BERLIN, GERMANY, ASSIGNOK 'IO TEIJilIEUNKEN GESELL- paratus.

SCHAFT FU'B DRAHTLOSE POBATION OF GERMANY TELEGBAP EIE MLB. 3., OF BERLIN, GERMANY, A COR -I-IEZO-ELEGTRIC acous'rxc DEVICE was..." filed my as, 1923, Serial we. w en, and m German-y September 1 -1927.

This invention relates to the piezo electric art and deals more specifically with an acoustic device employing a piezo electricfelement. It has already been proposed in the prior art to utilize the piezo electric effect in connection with microphonic and telephonic ap- For example, if sound waves are brought to act upon a suitably arranged piezo electric body bythe agency of a diaphragm,

a serious difficulty,

the pressure variations caused by the sound wave are directly converted into electrical oscillations, the electrical efi'ects being pro .portionalto the pressure brought ,to act upon the piezo electric body.

However, devices of this character involve that is, that the electrical actions are extremely feeble. It is therefore.

an object of this invention to provide an arrangement whereby the ensuing action can be considerably amplified.

Briefly, this object is attainedby the use I of a diaphragn'r in combination with a piezo surface.

electric body, the diaphragm being arched and arranged whereby the sound energy impinges upon said diaphragm and the m0- tional changes produced. thereby are converted into electrical impulses through the action of the piezo electric element; An arched diaphragm of this type produces amplified pressure forces in the direction of the surface, that is, motional forces come to act upon itscurved Curved or arched diaphragms per se are well known in the art, but the combination of such a curved diaphragm with a piezo electric device results in a particularly effective assembly for it is just a diaphragm -thus shaped which is particularly adapted directly to transfer upon the piezo electric body such strong pressureforces as are capable to substantially increase the electrical ac tion. Moreover, the resultant effects may be increased still further to a considerable comprising a plurality of superimposed piezo electric elements, so that the pressure brought to act upon the pile *of these piezo electric elements makes itself felt simultaneously on all of these bodies and accordingly tangentially whenever by means of a suitable circuit arrangement the individualelectrical effects of each crystal may be integrated in the external circuit.

The manner in which this invention is carried out willbe more clearly understood from the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a diagrammatic representation of da specific embodiment of this invention; an

Figs. 2 and 3 are diagrammatic views of modifications.

Referring .in' detail to Fig. 1,- the arched diaphragm 10 is fixedly supported at 11 and the end 10a of the diaphragm has joined to it an electrode 12, the electrode 12 being adapted to move in accordance with the mechanical vibrations of the crystal. A sec- .ond'el'ectrode 13 is fixedly joined to the support 14:. Intermediate of the plates 12 and '13 are the piezo electric crystal elements 15 suitably cut to give the desired electrical and mechanical characteristics. Intermediate of the elements 15 are the auxiliary plates or electrodes 12a, and 13a. The electrodes 12 and 12a are electrically connected and the electrodes 13 and 13a are electrically connected." A suitable amplifyingdevice. 20 is connected across'the electrodes 12 and 13.

The operation of'the device is as follows:

Sound impulses are made to impinge upon the diaphragm 10 and the motion of the vibrations produced thereby exerts a. tangential force which is applied to the electrode 12 and from this electrode to thecrystal elementsmounted between the electrode 12 and the fixed "electrode 13. The electrical oscillations resulting from the mechanical movement of the diaphragm are impressed upon the input circuit of the amplifier 20 and thus maybe amplified as desired.

In accordance with the modification of Fig. 2 thediaphragm 10 is mounted between two crystal units 30 and 31 each of which is similar in structure to the crystal assembly shown in Fig. 1 and which is provided with and 33. The elements30 and 32 the use of the additional crystal assembly more efficient transformation from sound impulses to electrical oscillations may be rezed. r e In a'- modification shown in Fig. 3 diaphragm 10 is supported between four crys-' tal assemblies or units indicated as 30, 31, 32

may be -con nected in parallel to an amplifier and the elements 31. and 33 may be connected in parallel to the same amplifier or to a separate amplifier'as desired.

It, will be understood, of course, that while the foregoing description relates to the op-. eration of the diaphragmand being converted into electrical oscillations, this device may be used" also in a reversiblesense as a loudspeaker. and

electrical oscillations impressed upon. the:

crystal units may be used to; actuate thev diaphragm to produce the necessary sound impulses. Many changes in the specific embodie ments disclosed herein will readily suggestv themselves to those skilled in the art and this.

,invention therefore is not to be limited inscope except as defined-in: the appended claims.

Having thus described my invention, I claim: i

1. An electroacoustic device comprising in combination, an arched vibratory dia phragm, a plurality of piezo-electric elements connected to opposite ends of said diaphragm, whereby mechanical vibrations applied tothe surface of said arched diaphragm are converted into tangential stresses, which stresses are exerted upon said piezo-electric elements to produce piezo-electrlc reactionsin accordance therewith.

2. An electroacoustic device comprlsing in, combination, an arched vibratory dia- ALEXANDER MEISSNER.

present device as a microphone, that is, that soundwaves impinging upon the v 

